Optical systems are used in optical lithography for patterning or "writing" on photoresist for lithographic masking operations. The resolution of these optical systems is inversely related to the wavelength used for the patterning or writing. In so-called direct-writing systems, where photoresist coated wafers are directly patterned by an optically-steered, focussed, beam of radiation rather than being exposed through a mask. The, the quality of the beam is as important as the wavelength of the beam for obtaining highest possible resolution, and, accordingly smallest possible feature size. Smaller features, of course, lead to higher component packing densities. One particularly useful light source for direct writing operations is an intracavity frequency-doubled argon ion-laser, having an output wavelength of 244 nm. Such a laser is used in a direct writing system manufactured by Etec, Inc., of Hayward, Calif.
Because of a continuing demand for ever smaller and faster semiconductor devices, there is a similar need for a laser system having a shorter wavelength than the 244 nm of existing direct-writing systems. Such a laser system, of course, should have a beam-quality comparable to existing 244 nm laser systems and provide sufficient power such that exposure times are not unacceptably protracted.